The present invention relates to a perpendicular magnetic recording method particularly, to a perpendicular magnetic recording method by which two or more kinds of signals can be superimposed on a recording medium.
A demand exists in the magnetic recording field for methods that can increase recording density, i.e. the ability to record great quantities of information on a compact recording medium. Recording density increase requires increase in the linear recording density as well as increases in track density.
The so-called longitudinal magnetic recording method is intended to lay magnetization in-plane and longitudinal direction of the recording medium and this method had been widely employed. In the case of the longitudinal magnetic recording method, high track density is made possible by using the tracking servo mechanism of high accuracy, etc. This method, however, has a limit in increasing linear recording density, because the demagnetizing field inside the recording medium increases, when the linear recording density is increased, thereby weakening the magnetization amplitude making it impossible to achieve a high quality recording. Therefore, the recording density or area recording density (recording amount per unit area of the recording medium) can not be increased dramatically.
On the other hand, the so-called perpendicular magnetic recording method is designed to use a recording medium which has an axis of magnetization in the depth (or perpendicular) direction, i.e. perpendicular magnetic anisotropy and to magnetize the recording medium in the depth (or perpendicular) direction thereof. This perpendicular magnetic recording method enables the linear recording density to be increased since the demagnetizing field inside the recording medium decreases as the linear recording density increases. This method, however, exibits different recording characteristics, from those for the longitudinal recording. Therefore, the perpendicular magnetic recording method can not employ the conventional track following servo techniques, such as a buried servo technique, which is one of the most advanced track following servo techniques used for the logntiduinal magnetic recording method. When compared with the longitudinal magnetic recording method, therefore, the perpendicular magnetic recording method can easily achieve a higher recording density but has a track density limit.